Advanced wireless communication systems and technologies require techniques to maximize spectral efficiency and data throughput to enable the transmission of large amounts of media content. The quest for ubiquitous networks with adaptive spectrum management calls for radio systems capable of processing multi-standard and multi-band signals. This has been traditionally addressed by deploying multiple dedicated transmitters/power amplifiers (PAs) to cover a given set of frequency bands. However, as the number of covered bands increases, this approach results in highly complex, large sized and expensive radio systems. A more suitable and cost efficient solution is to use one multi-band/multi-standard transmitter/PA to transmit a multi-band, multi-standard and multicarrier signal. While this approach addresses the disadvantage of the traditional solution, it brings challenges in terms of linearity and power efficiency.
In order to maximize spectral efficiency and data throughput, emerging wireless standards are yielding communication signals characterized by high peak-to-average power ratios (PAPR). Hence, future communication infrastructure will require highly power efficient, ultra-linear, multi-standard/multi-band radio systems. Recently, power efficiency enhancement techniques such as Doherty amplifiers and envelope tracking (ET) have been successfully applied to enhance the power efficiency of power amplifiers (PAs) driven with single-band modulated signals.
There have been several attempts to extend the Doherty amplifier to concurrent amplification of multi-standard/multi-band signals. This has been mainly attempted by extending the bandwidth of the Doherty amplifier to encompass more than one communication band, or by developing a Doherty amplifier capable of operating at two discrete frequencies.
Envelope tracking (ET) involves modulating the drain supply of the PA by an amplified envelope of the input signal. Envelope tracking has proven to be a serious contender to be a primary efficiency enhancement technique. However, efficiency and linearity analysis for ET have only been validated using single-band stimuli.